1. Field of the Invention
The present invention relates to a liquid coating apparatus, a liquid coating method and an image forming apparatus, and more particularly to liquid application technology which is suitable as a device for depositing a treatment liquid on a recording medium with the object of promoting aggregation of coloring material or the like, prior to ejecting ink droplets in an inkjet recording apparatus, and to an image forming apparatus which uses this technology.
2. Description of the Related Art
In order to achieve higher image quality for the printed image in the field of inkjet recording apparatuses, the use has recently become known of a liquid coating mechanism that applies a coating liquid (treatment liquid) that induces aggregation of the ink colorants on the surface of the printed medium; this application is carried out prior to the application of the inkjet image. A liquid coating mechanism is disclosed in Japanese Patent Application Publication No. 2007-83180 that takes into account the coatability on target media (recording media) that have a relatively small size, e.g., sheet-form paper, as well as the prevention of liquid leakage due to changes in position during transport by the apparatus. This liquid coating mechanism is provided with a coating roller that rotates in contact with the recording medium and a liquid holding member that holds the coating liquid in a liquid holding space that is formed with the roller surface by abutment with the circumference (coating surface) of the coating roller.
The liquid coating apparatus described in Japanese Patent Application Publication No. 2007-83180 has a structure in which, through rotation of the coating roller, coating liquid is transferred onto the recording medium from the coating medium while coating liquid is also fed to the coating surface of the coating roller from the liquid holding space.
However, in the liquid coating apparatus disclosed in Japanese Patent Application Publication No. 2007-83180, the coating surface of the roller comes into direct contact with the backup roller (the backup roller is positioned on the back surface of the paper sheet) between one paper sheet and the ensuing paper sheet, which results in contamination of the apparatus and in extreme cases produces leakage by the liquid and may also result in contamination of the back surface of the paper sheet by retransfer of the treatment liquid from the backup roller.
In addition, while the formation of a liquid puddle (known as a bead) between a medium (sheet-form paper) and a coating roller enables the elaboration of a uniform coating at a prescribed film thickness in a coating step that uses a coating roller, this liquid bead is unstable in the case of the leading edge region of intermittently fed paper sheet, making uniform coating quite problematic.